fix: xgboost raw parser (#518)

LGTM

Author: cdmbr

src/main/java/com/o19s/es/ltr/ranker/parser/XGBoostRawJsonParser.java

@@ -25,8 +25,6 @@ public class XGBoostRawJsonParser implements LtrRankerParser {
 
     public static final String TYPE = "model/xgboost+json+raw";
 
-    private static final Integer MISSING_NODE_ID = Integer.MAX_VALUE;
-
     @Override
     public NaiveAdditiveDecisionTree parse(FeatureSet set, String model) {
         XGBoostRawJsonParser.XGBoostDefinition modelDefinition;
@@ -439,8 +437,16 @@ private NaiveAdditiveDecisionTree.Node asLibTree(Integer nodeId) {
             }
 
             if (isSplit(nodeId)) {
-                return new NaiveAdditiveDecisionTree.Split(asLibTree(leftChildren.get(nodeId)), asLibTree(rightChildren.get(nodeId)),
-                        splitIndices.get(nodeId), splitConditions.get(nodeId), splitIndices.get(nodeId), MISSING_NODE_ID);
+                Integer missingNodeId =
+                    defaultLeft.get(nodeId) == 1 ? leftChildren.get(nodeId) : rightChildren.get(nodeId);
+                return new NaiveAdditiveDecisionTree.Split(
+                    asLibTree(leftChildren.get(nodeId)),
+                    asLibTree(rightChildren.get(nodeId)),
+                    splitIndices.get(nodeId),
+                    splitConditions.get(nodeId),
+                    leftChildren.get(nodeId),
+                    missingNodeId
+                );
             } else {
                 return new NaiveAdditiveDecisionTree.Leaf(baseWeights.get(nodeId));
             }